The U.S. Federal Bureau of Investigation (FBI) has started probing financial assistance received from abroad so far by religious schools in Pakistan and also by militant or jihadi organisations of the country.

The government had earlier allowed the U.S. to share information on money received in the country through unofficial channels like 'hundi' or 'hawala', sources here said, citing the recent restrictions on financial transactions imposed as part of the U.S.-led campaign against terrorism.

A high-powered team of investigators from America, after meetings in Islamabad, has come to Karachi to collect details from the country's central State Bank, private and government banking and financial institutions, and currency dealers.

"They have been meeting a lot of people to find out as to the financial backing of madrassas operating in Pakistan, and also militant organisations who were in the forefront of Afghanistan war, and had links with Osama bin Laden and his Al Qaida group," said the sources.

Americans believe that the hundi or hawala were the biggest sources of income for the militants in Pakistan, and their patrons in Afghanistan.

The Pakistan government had tried for years together to discourage Pakistanis living abroad from sending money through unofficial channels, but the temptation of premium on conversion rate for remittances, was so great that the advice given by Islamabad, fell on deaf ears.